This invention relates to a new and useful impact device adaptable to being driven by a portable electric drill. The impact device employs a rotating cam impeller to reciprocate a chisel-type tool or bit into intermittent contact with a work surface.
The known portable impact devices produce large amounts of reverse thrust during each impact cycle, which can easily lead to excessive operator fatigue as well as premature failure of the support bearing structure positioned within the impact device and also driving member's thrust-bearings and structure.
As for example, U.S. Pat. No. 2,211,741, issued Aug. 13, 1940, to Elwell, discloses an impact device that is typical of the prior art. The Elwell device uses a compression spring to maintain contact between the drive cam and the reciprocating tool. This requires the operator to exert a pulling force on the handle and attached casing while simultaneously exerting all the pushing force on the drive cam through the attached driving source in order to maintain contact between the drive cam and reciprocating tool. The required push-pull operation quickly fatigues the operator while limiting the total amount of pressure which can be exerted against the work surface through the tool.
The Elwell structure cannot be operated as a variable stroke, impact device because of the action of the biasing spring. Furthermore, the roller bearing assembly attached to the reciprocating tool is susceptible to premature failure due to the large thrust forces generated during impact. Finally, the thrust forces plus the pulling force equal to the spring resistance generated during impact act directly against the drive motor bearings causing damage to both the impact device and the attached drive source.
As will be discussed in detail hereinafter, applicant's new and useful invention solves the problems confronting the prior art, while at the same time providing an inexpensive variable stroke impact device wherein the entire operator pressure is exerted against the work surface through the tool.